1. Technical Field
The present invention relates to printing methods, printing apparatuses, printing control apparatuses, and storage media.
2. Related Art
A printing apparatus such as an inkjet printer prints an image to be printed on a medium by alternately repeating a dot forming process for forming dots by ejecting ink from a nozzle that moves in a moving direction, and a carrying process for carrying a medium such as paper in a carrying direction, thereby successively arranging in the carrying direction raster lines that are configured by a plurality of dots lined up in the moving direction.
In order to increase the print speed, it is desirable to increase the number of nozzles so that the number of raster lines formed by a single dot forming process can be increased. Therefore, it is proposed to provide a plurality of nozzle groups in the head so as to increase the number of nozzles easily (See JP-A-10-323978).
While printing methods such as “interlace printing” or “overlap printing” are known, there is another printing method called “non-uniform overlap printing” (See JP-A-2002-11859). In this “non-uniform overlap printing”, the number of nozzles used to form a raster line differs according to the raster line. For example, two nozzles are used to form a certain raster line, but three nozzles are used to form another raster line.
When the “non-uniform overlap printing” is performed using a plurality of nozzle groups, for example, it is possible that a certain raster line is formed by one nozzle of a first nozzle group and one nozzle of a second nozzle group, and another raster line is formed by two nozzles of the first nozzle group and one nozzle of the second nozzle group. In the latter raster line, the number of dots formed by the nozzles of the first nozzle group is larger than that formed by the nozzles of the second nozzle group.
In other words, as the latter raster line, when the number of nozzles used to form a certain raster line differs for each nozzle group, the ratio of dots formed by the nozzles of a nozzle group that is a part of a plurality of nozzle groups may increase. As a result, that certain raster line reflects a strong effect of that particular nozzle group. When raster lines reflect strong effects of different nozzle groups, if the ink ejection characteristic of each nozzle group differs due to influence of irregularity in manufacturing, etc., densities in resultant raster lines may be inconsistent, and a striped pattern may appear in the printed image.